I have a 1992 230TE. Only had the car one year. Body and underneath is excellent so I think that it has been looked after. When I come to a hill the power drops off dramatically and I can only go at about 45 MPH. I have noticed that the idle valve?? is not connected to its wiring plug. When I plug it in, the car will start but will not idle and stalls. I have fitted a new fuel filter and ignition leads, but it has made no difference at all. This is my first Mercedes so do not know much about them. Can anyone Help??

A W124 with an M102 engine was never known for an abundance of power, but obviously in your case there is a genuine problem making matters worse. I believe a clue lies in the fact that you mention the idle control valve is disconnected and that the engine stalls with it connected. This suggest a problem with the ECU or the engine speed signal sent to it. Given that you get this effect when connecting the ICV suggests that the ECU is at least getting power, which tends to rule out the over-voltage protection relay and its associated fuse. If you are comfortable with diagnosing this yourself, read Steve Brotherton's article "Evaluating Electronic Engine Controls" in the DIY section of this site. This explains how to check for correct closed loop operation of the KE-Jetronic injection fitted to your car. This will at least indicate to you whether or not the ECU is controlling the air/fuel ratio which could go some way to explaining a lack of power. How does it behave otherwise? Does it start easily hot and cold? How is the fuel consumption? The bigger the picture of any symptoms, the better the chance of diagnosing the problem. If you are not comfortable with this diagnostic evaluation yourself, I would strongly recommend taking it to someone who genuinely understands KE-Jetronic, otherwise you could end up throwing a lot of money at wasted labour and unnecessary parts.

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.